Why is it that when you cut on the air or heat in my truck its starts idling bad?

Most likely one of two things need checking. #1 make sure your fan assembly is working properly. This means that the fan is turning and not sticking or off completely. However in this case you would be experiencing "running hot" while idiling at red lights. #2 Your MAF ( main air flow) it could be clogged or your sensor might be dirty. To see if this is the case, go to your parts store and buy a can of SEAFOAM. It runs about $10 a can. Empty it in your gas tank on E fill up with atleast mid grade gas this time. Run it on the interstate hard for 15-20 minutes or so. Once you get back on street roads if the hard idle has stopped then you will need to get a cleaner spray for the MAF sensor or let a repair shop clean it for you, but it will cost considerably more of course.

The HVAC ( heating, ventilation, air conditioning) servos use engine vacuum to operate, you may have a fairly large vacuum leak in the HVAC system.